Laserfiche WebLink
2.4. INPUT PARAMETERS <br />2.4.1. Hydraulic Conductivities <br />Hydraulic conductivity for the lower gravel layer was set to 600 ft/day (Sy=0.2). <br />The value has been accepted by the Colorado Office of the State Engineer as a <br />representative value for gravel deposits on the Big Thompson River. The <br />conductivity of the upper silt and clay layer was set to 10 ft/day. The conductivity <br />of reclamation fill materials to be placed after mining is completed was set to 10 <br />ft/day (Sy=0.1). The clay liner for the reclaimed east pit in the model has a <br />hydraulic conductivity of 0.003 ft/day as is required by the State Engineer. <br />2.4.2. jg Thompson River <br />The Big Thompson River is simulated through application of a Constant Head <br />boundary in MODFLOW. WI surveyed the riverbed and banks in June of 2003 <br />for a separate Floodplain Modeling effort. This river water level survey data was <br />used as the basis for the constant head elevations in each river cell of the model. <br />2.4.3. Thompson Ponds <br />The Big Thompson Ponds are simulated through application if the LAKES <br />package in MODFLOW. They are designated lakes #1 through #4 in the model. <br />The Iakebed hydraulic conductivity was set at 3 ft/day and the lakebed thickness <br />was set at 2 feet. The lake stage was set to 5 ft above lakebed bottom <br />elevations. <br />2.4.4. Hillsborough Ditch <br />The Hillsborough Ditch is simulated through application if the General Head <br />Boundary package in MODFLOW. <br />The conductance multiplier for each cell of the ditch (GHB cells) was set at 1.25 <br />ft/day. The head for each cell was set at an elevation of 4853 feet. This elevation <br />assumes a 4 ft ditch depth as measured from the high water mark at the box <br />culvert under 1-25. This represents the average stage level of the ditch through <br />the model study area. <br />2.4.5. West Pit Dewaterinq <br />Dewatering of the pit is simulated through application of the DRAIN package in <br />MODFLOW. Each model cell on the perimeter of the pit is simulated as a drain <br />cell. Mining will proceed in two phases: first a west pit will be mined and <br />reclaimed then an east pit will be mined and reclaimed. <br />Flying W Pit <br />Groundwater Modeling Report Revised June 28, 2005 <br />5of13 <br />